USB vs S/PDIF
Printed From: Graham Slee Hifi System Components
Category: Digital Audio
Forum Name: Computer Audio
Forum Description: Is computer audio here to stay or is it just another flavour of the month?
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=4976
Printed Date: 27 Mar 2026 at 5:57am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: USB vs S/PDIF
Posted By: Ash
Subject: USB vs S/PDIF
Date Posted: 16 Jun 2020 at 7:58pm
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So is optical or coaxial really a higher fidelity interface than USB (with linear power supply, not bus power)? I mean by Slee design standards. I would be interested to read Graham's reasoning on this question. Is toslink/coax worth pursuing or is the grass not always greener? The purpose of digital audio is to be streamed to a receiver and USB seems to be the modern standard for transferring data between devices. Why aren't optical/coax used for devices like external hard drives? Is it just the convenience of USB having both power and signal in one cable rather than connecting two separate cables? Surely there is a rationale why Graham only gave the Bitzie USB input...
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Replies:
Posted By: BackinBlack
Date Posted: 16 Jun 2020 at 8:15pm
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If I recall correctly, wasn't the Bitzie conceived as a "digital" version of the Voyager. If so, the typical input was to be USB from a mobile device, very few, if any, having S/PDIF outputs. The inclusion of S/PDIF would have also added to the physical size which is critical for a mobile device. As to which is superior, USB or S/PDIF. I think it depends very much on the devices concerned. I shall remain on the fence. Ian ------------- Just listen, if it sounds good to you, enjoy it. |
Posted By: BackinBlack
Date Posted: 16 Jun 2020 at 8:20pm
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The Bitzie story starts here: https://www.hifisystemcomponents.com/forum/usb-dac-a-digital-voyager_topic1444.html - https://www.hifisystemcomponents.com/forum/usb-dac-a-digital-voyager_topic1444.html ------------- Just listen, if it sounds good to you, enjoy it. |
Posted By: Graham Slee
Date Posted: 16 Jun 2020 at 10:35pm
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I think USB is more consistent between different host devices, but I only tried the Bitzie and Majestic as receivers. I tried a number of S/PDIF sources into the Majestic, and all had a different sound, and I guess that's how it is. It can be transformer driven or resistively driven, coax or optical, and it might be level translated, and if so, could be one of a number of logic chips and/or gating arrangements, all with different propagation timing, and even ringing (or not) on the waveform. Even with the excellent features of the WM8804 transceiver doing the S/PDIF receiving, it has to lock onto the clock which might not be so well defined as it could. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Ash
Date Posted: 16 Jun 2020 at 10:58pm
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Thank you. I have always got great results out of Bitzie and Majestic from USB, especially Majestic into Proprius and earspeakers. Some USB ports exhibit more noise than others. I guess, as usual, only a little can be learned by talking and the rest has to be found by doing and experiencing. Shall sell some stuff for funds then have a play with some more single board computers that are fanless and I can add a linear PSU. Looking at the HDPlex PSU as a possible candidate for future testing. Great thing about the Majestic is the number of inputs available, which can potentially be compared side-by-side at the turn of a dial.
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Posted By: Ash
Date Posted: 17 Jun 2020 at 7:48am
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With regards to my first post, a very important point that I missed is that data transfer can be bidirectional in USB whereas optical/coax are for unidirectional data transfer only, so not suitable for storage media where you need the facility to both send and recall. Maybe isochronous USB, with its 'guaranteed timing', is the most reliable and consistent interface despite having a smaller sample rate bandwidth than S/PDIF options.
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Posted By: Graham Slee
Date Posted: 17 Jun 2020 at 8:23am
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I'm no computer expert. All I know is isochronous USB audio is sent in "packets" consisting of ID and other clever preamble bits, a "snippet" of PCM audio, n-bits long, and an end-point. It seems to have "excess baggage." Somehow, the USB CODEC throws away the unwanted bits, leaving snatches of audio, which are shoved into a buffer, and emerge as a stream. In the case of data outputted, it is in S/PDIF form, but at logic levels. The only thing "fed back" to the host is HID instructions such as volume control, which I "null." If the host sends a glitch, the glitch might screw the music around, or add noise, but I've not been able to hear it. Otherwise, it just keeps playing, and the "rules" are such that it does. I once had a knackered PC, which while playing, stopped doing the other things I wanted it to do, and hung. It kept playing correctly until it blue-screened and shut down - for good. Audiophiles say they prefer asynchronous because it handshakes, which is supposed to make it sound better because it's more accurate. But if it doesn't verify, it stops playing while it sorts it out. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: VinodCrispon
Date Posted: 22 Jun 2020 at 5:38pm
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Hi Graham, I too agree that SPDIF Sound quality varies with components. Initially I was under the impression a cheap CD Transport or Network Streamer with Coax out is sufficient, Save & Invest on a good DAC. How much more can I go wrong.  . I now strongly believe a DAC cannot improve on what is not there, and definitely "Majestic" is not doing that. (Probably much easier to manipulate the signals in the DAC for the newer FPGA Software controlled DAC Technologies)Considering your experience on S/PDIF sounding different in different sources, how Pure is the Digital out of the S/PDIF. In this context do you feel the I2S will be a better source of Digital Signal vs coax or Optical. Also what are the advantages of the AES connector Vs the RCA Coax / Optical (SPDIF) signals. Considering the Majestic has so many Input options can a AES or I2S over HDMI will be an option that can be offered?  ------------- Vinod Vincent Elevator & Accession w PSU-1/ Majestic w Enigma/ Cusat/ Lautus TT: Amazon 1(Candenza Bronze) Amp: Accuphase E650 CD/Streamer: OPPO UDP205/CYRUS StreamX2 Speaker: Dynaudio Contour S3.4 |
Posted By: Graham Slee
Date Posted: 22 Jun 2020 at 9:24pm
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My experience of I2S is to keep the inter-IC connections as short as possible, which in the Majestic "DAC Engine" is about 1.5 inches. I cannot imagine I2S becoming an interconnect cable. AES is the professional standard for studios where the XLR reigns supreme. Still, it has to terminate to single ended. It has a matching impedance of 110 ohms. S/PDIF, using 75 ohm coax, is terminated 75 ohms. Not much more to say. A good (fast) transformer, either or both ends, tends to ensure a clean signal. Optical is limited by data rate to 96kHz, but can be encoded and decoded at logic levels, which is far cleaner in my opinion. I think you'll find it is nothing to do with these items, but the way the transport is implemented. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Aussie Mick
Date Posted: 22 Jun 2020 at 11:51pm
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Hi Graham, Thanks for your recent explanations of these connections. They ring true with a few other things I’ve read from other respected designers. In particular on the cleanness of optical, one quite prominent DAC designer who shares your view has been heavily criticised by the blogging types for voicing such an opinion. Your explanation makes perfect sense. One often wonders what happened to the naysayers in early life to make them so bitter and suspicious. Thanks for your work, Mick. ------------- Rega RP8 - Apheta 2 - Accession MC Enigma PS -Solo ULDE (Focal Utopia) - PS Audio M700 - Fical Kanta No2 |
Posted By: VinodCrispon
Date Posted: 24 Jun 2020 at 4:56pm
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Hi Graham, Thanks for the feedback on the different interconnects. With regards to the Optical. Last year I had the opportunity to meet Rob Watts, he also share the same opinion on Optical as yours. But I am yet to try a good sounding optical connection, It was always bright sounding for my taste. Unfortunately during the event arranged by the local dealer, out of 60mins he spoke for 57 mins and 3mins they played an electronic track, I ended up returning with so much of Theory on FPGA than how their DAC sounded. Am happy it happened that way. No further confusions, I just decided to blindly take the Leap with Majestic. And I am happy I did it. I am all 'Slee'ed' again. ------------- Vinod Vincent Elevator & Accession w PSU-1/ Majestic w Enigma/ Cusat/ Lautus TT: Amazon 1(Candenza Bronze) Amp: Accuphase E650 CD/Streamer: OPPO UDP205/CYRUS StreamX2 Speaker: Dynaudio Contour S3.4 |